The effect of Nano-fibrillated cellulose on the mechanical properties of polymer films.

Transcription

1 The effect of Nano-fibrillated cellulose on the mechanical properties of polymer films. Gerard Gagnon, Rikard Rigdal, Jake Schual-Berke, Mike Bilodeau and Douglas W. Bousfield Department of Chemical and Biological Engineering and the Process Development Center University of Maine Orono, ME USA EXTENDED ABSTRACT Nano-fibrillated cellulose (NFC) was produced mechanically from a bleached soft wood kraft fiber using a pre-treatment method followed by refining or homogenization. Field emission scanning electron microscope images of the material reveals a large number of fine scale fibers with diameters between nm and lengths of over a micron. Polymer films were produced by mixing NFC with a styrene-butadiene latex or polyvinyl alcohol. Films were cast onto Teflon coated aluminum foil and dried under heat lamps. A mechanical tester characterized the elastic modulus of the films, the ultimate tensile strengths, and the rupture strains. Figure 1 compares the stress strain results of the pure latex film with the film that contains 18% by weight NFC. The pure latex has a large region of regular stretching and a high rupture strain. The addition of NFC increases the elastic modulus, decreases the rupture strain and has little effect on the ultimate tensile strength. Similar results are seen for the polyvinyl alcohol films. Figures 2 and 3 show the Young s modulus for the latex and polyvinyl alcohol films, respectively. The yield point increased for latex films with increasing amounts of NFC while no trend was observed for polyvinyl alcohol films.the influence of citric acid addition on these films is also reported. There is significant scatter in the data as can be seen in the repeat results and the error bars. Figure 1. Results of pure latex film (left) and a film with 18% NFC by weight (right). Different curves are for different samples but of the same composition.

2 Young's Modulus (MPa) wt% 3.9wt% 9.5wt% 14.8wt% 18.2wt% NFC Loading Level Figure 2. Young s modulus for latex films at different NFC loading Young's Modulus (MPa) wt% 2wt% 5wt% 8wt% 10wt% NFC loading level Figure 3. Young s modulus for polyvinyl alcohol films with various levels of NFC. While the addition of NFC to these polymers did increase the modulus, the strain to failure decreased. This can be seen in Fig.1 and noting the different ranges for the x axis. NFC clearly makes a stiffer material. The ultimate tensile strength is not a strong function of NFC content. The NFC used in this study has a wide particle size distribution. Therefore, even a few large particles could misrepresent the content of nano-scale material. In addition, larger material may give rise to weak points within the structure. However, NFC is clearly shown here to have the ability to produce a more rigid polymer film.

3 The Effect of Nano-Fibrillated Cellulose on the Mechanical Properties of Polymer Films Gerard R. Gagnon Jr., Rikard Rigdal, Jake Schual-Berke, Michael Bilodeau and Douglas W. Bousfield Department of Chemical and Biological Engineering University of Maine

4 Introduction Nano-fibrillated cellulose (NFC) may be used for medical devices reinforcing agent in plastic composites food additive paper & coatings cosmetic products dispersions & emulsions. 1,2 NFCs as a reinforcing agent in composites can increase strength lower material cost NFCs are compatible with water-based polymer systems, such as styrene-butadiene (SBR) latex and polyvinyl alcohol (PVOH) 1 Adv Polym Sci 205 (2006) 49-96, 2 Materials Science and Engineering A 490 (2008) , 2

5 Materials Used for Producing Nanofiber Reinforced Polymer Films Nanofibers were produced by mechanical treatment of cellulose fibers, with and without a chemical pre-treatment. The chemical pre-treatment of NFC consisted of partially hydrolyzing the fiber with MgCl 2 and heat. SBR latex films with chemically pre-treated NFC were produced. Polyvinyl alcohol (PVOH) films with and without chemically pre-treated NFC were produced. 3

6 Materials Used for Producing Nanofiber Reinforced Polymer Films SBR latex Tg of 10 o C Particle size 150 nm PVOH molecular weight - 85,000 to 124,000 g/mol >99% hydrolyzed 4

7 Materials Used for Producing NFC Reinforced Polymer Films FE SEM image of chemically pre-treated nanofibrillar cellulose 5

8 Method of Preparing Latex / NFC Films A draw down method was developed to prepare SBR latex/nfc composites Wire wound rod used to form wet film. Film dried under heat lamps to avoid cracking and trapping air. Samples of films cut between two sheet of paper at an elevated temperature to avoid cracking. Coating Direction Wire Wound Coating Rod Films of PVOH were prepared by drying aqueous mixtures of PVOH/NFC in a thin open mold of Mylar sheets under a heat lamp. Teflon Coated Aluminium Foil Rikard Rigdal ml of Liquid 6

9 Tensile Testing Rectangular samples were cut from each film parallel to the draw down direction. Tensile tests were performed using a standard laboratory tensile tester. Averages are from at least 6 samples per condition. Rikard Rigdal

10 SBR Latex & NFC Films: Tensile Testing Results Static Tensile Test NFC Static Tensile Test SBR only Rikard Rigdal 2008 NFC film demonstrated a linear elastic region up to the rupture strain. The elastic modulus of NFC film is significantly higher than for the pure SBR latex film. 8

11 Mechanical Properties of SBR Latex Films Containing Chemically Pre-treated NFC Young's Modulus (MPa) wt% 3.9wt% 9.5wt% 14.8wt% 18.2wt% NFC Loading Level The Young s Modulus increased for the two highest addition levels of NFC 9

12 Mechanical Properties of SBR Latex Films Containing Chemically Pre-treated NFC % Ultimate Tensile strength (MPa) Rupture Strain (%) 150% 120% 90% 60% 30% 0 0wt% 3.9wt% 9.5wt% 14.8wt% 18.2wt% NFC Loading Level 0% 0wt% 3.9wt% 9.5wt% 14.8wt% 18.2wt% NFC Loading Level The addition of pre-treated NFC to SBR latex films did not significantly impact the ultimate tensile strength. Rupture stress decreases with increasing NFC concentration. The composites were becoming increasingly more brittle. 10

13 Mechanical Properties of PVOH Films Containing Untreated NFC Young's Modulus (MPa) wt% 2wt% 5wt% 8wt% 10wt% NFC loading level Young s modulus of PVOH films increased at the highest loading of NFC. 11

14 Mechanical Properties of PVOH Films Containing Untreated NFC 60 70% Ultimate Tensile Strength (MPa) wt% 2wt% 5wt% 8wt% 10wt% NFC Loading Level 0wt% 2wt% 5wt% 8wt% 10wt% NFC Loading Level NFC loading did not significantly impact the ultimate tensile strength. The two highest loadings of NFC resulted in more brittle PVOH films, requiring much less strain to break. Rupture Strain (%) 60% 50% 40% 30% 20% 10% 0% 12

15 Mechanical Properties of PVOH Films Containing Chemically Pre-treated NFC Young's Modulus (MPa) wt% 1wt% 2wt% 5wt% Loading level Young s Modulus showed a modest increase at the higher pretreated NFC concentrations. 13

16 Mechanical Properties of PVOH Films Containing Chemically Pre-treated NFC 70 Utlimate Tensile Strength (MPa) wt% 1wt% 2wt% 5wt% NFC Loading llevel Adding chemically pre-treated NFC to PVOH films did not significantly improve the ultimate tensile strength. 14

17 SBR Latex / Kaolin / NFC Films: Mechanical Properties + 5 wt% NFC + 2 wt% NFC SBR & kaolin (50/50) Rikard Rigdal 2008 SBR latex, kaolin and pretreated NFC films had higher tensile strength and Young s Modulus than SBR latex and kaolin films. 15

18 Summary For SBR latex composite films, increasing NFC content increased Young s Modulus no significant impact on the ultimate tensile strength decreased the rupture strain. 16

19 Summary For PVOH composite films, increasing NFC content increased Young s Modulus no significant impact on the ultimate tensile strength decreased the rupture strain. Chemically pre-treating NFC showed no significant impact on reinforcement properties compared to untreated NFC. 17

20 Summary For SBR latex & kaolin composite films, increasing NFC content increased Young s Modulus increased ultimate tensile strength decreased the rupture strain. 18

21 Questions 19